While direct surgical and percutaneous revascularization through procedures such as a percutaneous transluminal coronary angioplasty (“PTCA”) or coronary artery bypass grafting (“CABG”) remain the mainstay of treatment for patients with angina and coronary artery disease (“CAD”), there are many patients that are not amenable to such conventional revascularization therapies. Because of this, much effort has been made to find alternative methods of revascularization for ischemic cardiac patients who are not candidates for revascularization by conventional techniques. Such patients are generally identified as “no-option” patients because there is no conventional therapeutic option available to treat their condition. As described in detail herein, the present disclosure provides various embodiments of devices to address such chronic conditions.
In addition, and as described in detail herein, the present disclosure provides various embodiments of devices that can be used acutely to treat patients with a number of conditions, such as S-T segment elevated myocardial infarction (STEMI) or cardiogenic shock or patients who require high risk percutaneous coronary intervention, until they can receive more traditional therapy.
Currently, there are multiple specific conditions for which conventional revascularization techniques are known to be ineffective as a treatment. Two specific examples of such cardiac conditions include, without limitation, diffuse CAD and refractory angina. Furthermore, a percentage of all patients diagnosed with symptomatic CAD are not suitable for CABG or PTCA. In addition and for various reasons discussed below, diabetic patients—especially those with type 2 diabetes—exhibit an increased risk for CAD that is not effectively treated by conventional revascularization techniques.
There is currently little data available on the prevalence and prognosis of patients with symptomatic CAD that is not amenable to revascularization through conventional methods. However, one study indicated that out of five hundred (500) patients with symptomatic CAD who were considering direct myocardial revascularization and angiogenesis, almost twelve percent (12%) were not suitable for CABG or PTCA for various reasons. Furthermore, in general, patients with atherosclerotic involvement of the distal coronary arteries have high mortality and morbidity. For example, a study conducted on patients indicated that, one (1) year after being diagnosed with atherosclerotic involvement of the distal coronary arteries, 39.2% of such patients had a cardiac-related death, 37.2% had an acute myocardial infarction, and 5.8% had developed congestive heart failure. Overall, 82.2% of the patients with atherosclerotic involvement of distal coronary arteries had developed or experienced a significant cardiac event within one (1) year.
A. Diffuse CAD and Refractory Angina
CAD is typically not focal (i.e. limited to one point or a small region of the coronary artery), but rather diffused over a large length of the entire vessel, which is termed “diffuse CAD.” Several studies indicate that patients with a diffusely diseased coronary artery for whom standard CABG techniques cannot be successfully performed constitute about 0.8% to about 25.1% of all patients diagnosed with CAD. Furthermore, it is believed that diffuse CAD is much more common than conventionally diagnosed because it is often difficult to detect by an angiogram due to the two-dimensional views.
Practitioners have realized that the quality of a patient's distal coronary arteries is one of the critical factors related to a successful outcome of a surgical revascularization. As previously indicated, there is considerable evidence that CABG for vessels having diffuse CAD results in a relatively poor outcome. In fact, studies have indicated that diffuse CAD is a strong independent predictor of death after a CABG procedure. Further, as previously noted conventional revascularization techniques have also proven ineffective on a subgroup of patients with medically refractory angina. In line with the aforementioned reasoning, this is likely because patients with medically refractory angina have small or diffusely diseased distal vessels that are not amenable to conventional revascularization therapies. Accordingly, patients exhibiting diffuse CAD or medically refractory angina are often considered no-option patients and not offered bypass surgery, PTCA, or other conventional procedures.
B. Diabetes as a Risk Factor
Diabetes is an important risk factor for the development of CAD, diffuse or asymptomatic, and it has been estimated that approximately seventy-five percent (75%) of the deaths in diabetic patients are likely attributed to CAD. It is estimated that 16 million Americans have diabetes, without only 10 million being diagnosed. Patients with diabetes develop CAD at an accelerated rate and have a higher incidence of heart failure, myocardial infarction, and cardiac death than non-diabetics.
According to recent projections, the prevalence of diabetes in the United States is predicted to be about ten percent (10%) of the population by 2025. Further, the increasing prevalence of obesity and sedentary lifestyles throughout developed countries around the world is expected to drive the worldwide number of individuals with diabetes to more than 330 million by the year 2025. As may be expected, the burden of cardiovascular disease and premature mortality that is associated with diabetes will also substantially increase, reflecting in not only an increased amount of individuals with CAD, but an increased number of younger adults and adolescents with type 2 diabetes who are at a two- to four-fold higher risk of experiencing a cardiovascular-related death as compared to non-diabetics.
In addition to developing CAD at an accelerated rate, CAD in diabetic patients is typically detected in an advanced stage, as opposed to when the disease is premature and symptomatic. Consequently, when diabetic patients are finally diagnosed with CAD they commonly exhibit more extensive coronary atherosclerosis and their epicardial vessels are less amendable to interventional treatment, as compared to the non-diabetic population. Moreover, as compared with non-diabetic patients, diabetic patients have lower ejection fractions in general and therefore have an increased chance of suffering from silent myocardial infarctions.
C. No-Option Patients
Some studies have shown that two-thirds (⅔) of the patients who were not offered bypass surgery, because of diffuse CAD or otherwise, either died or had a non-fatal myocardial infarction within twelve (12) months. Furthermore, patients diagnosed with diffuse CAD ran a two-fold increased risk of in-hospital death or major morbidity, and their survival rate at two (2) years was worse than those patients who exhibited non-diffuse CAD or other complicating conditions. As previously indicated, the majority of these patients are considered no-option patients and are frequently denied bypass surgery as it is believed that CABG would result in a poor outcome.
Due to the increasing numbers of no-option patients and a trend in cardiac surgery towards more aggressive coronary interventions, a growing percentage of patients with diffuse CAD and other no-option indications are being approved for coronary bypass surgery because, in effect, there are no other meaningful treatment or therapeutic options. Some effects of this trend are that the practice of coronary bypass surgery has undergone significant changes due to the aggressive use of coronary stents and the clinical profiles of patients referred for CABG are declining. As such, performing effective and successful coronary bypass surgeries is becoming much more challenging. Bypass grafting diffusely diseased vessels typically requires the use of innovative operations such as on-lay patches, endarterectomies and more than one graft for a single vessel. Patients with “full metal jackets” (or multiple stents) are typically not referred to cardiac surgeons and often end up as no-option patients despite the attempts of using these innovative surgeries.
In recent decades, the spectrum of patients referred for CABG are older and are afflicted with other morbidities such as hypertension, diabetes mellitus, cerebral and peripheral vascular disease, renal dysfunction, and chronic pulmonary disease. In addition, many patients referred for CABG have advanced diffuse CAD and have previously undergone at least one catheter-based intervention or surgical revascularization procedure that either failed or was not effective. Because of this, the patient's vessels may no longer be graftable and complete revascularization using conventional CABG may not be feasible. An incomplete myocardial revascularization procedure has been shown to adversely affect short-term and long-term outcomes after coronary surgery.
Due in part to some of the aforementioned reasons, reoperative CABG surgery is now commonplace, accounting for over twenty percent (20%) of cases in some clinics. It is well established that mortality for reoperative CABG operations is significantly higher than primary operations. As such, the risk profile of reoperative patients is significantly increased and such patients are subjected to an increased risk of both in-hospital and long-term adverse outcomes.
Further, clinicians have also turned to unconventional therapies to treat non-option patients. For example, coronary endarterectomy (“CE”) has been used as an adjunct to CABG in a select group of patients with diffuse CAD in order to afford complete revascularization. However, while CE was first described in 1957 as a method of treating CAD without using cardiopulmonary bypass and CABG, this procedure has been associated with high postoperative morbidity and mortality rates and has been afforded much scrutiny. Nevertheless, CE is the only therapeutic option available for many no-option patients with diffuse CAD.
Similarly, because conventional therapies have proven ineffective or are unavailable to high risk patients, perioperative transmyocardial revascularization (“TMR”) has been indicated for patients suffering from medically refractory angina. TMR has proven effective for most patients suffering from refractory angina; the mortality rate after TMR in patients with stable angina ranges between about one to twenty percent (1-20%). Furthermore, in one study, TMR resulted in a higher perioperatively mortality rate in patients with unstable angina than those with stable angina (27% versus 1%). Some even report an operative mortality rate as low as twelve percent (12%). Patients who experience angina and who cannot be weaned from intravenous nitroglycerin and heparin have a significantly higher operative mortality rate (16-27% versus 1-3%). Based on these findings, the clinical practice has been to avoid taking such patients to the operating room for TMR if at all possible. The success of TMR is thought to be due to improved regional blood flow to ischemic myocardium, but the precise mechanisms of its effects remain unclear.
D. Acute Applications
When a coronary artery becomes blocked, the flow of blood to the myocardium stops and the muscle is damaged. This process is known as myocardial infarction (MI). An MI can damage the myocardium, resulting in a scarred area that does not function properly. MI has an annual incidence rate of 1.5 million in the US and is the primary driver of roughly 500,000 cases of mortality and high morbidity rates in CAD patients. Immediate reperfusion of the myocardium following MI is clinically desirable to preserve as much heart tissue as possible. Current revascularization options include thrombolytic medications, percutaneous coronary intervention (PCI), or coronary artery bypass graft (CABG). While thrombolytic compounds can be administered swiftly in an acute care facility, the vast majority of MI patients require a PCI or CABG to adequately restore reliable blood flow to the heart tissue. Both of these revascularization techniques are clinically safe and effective, however, they require specialized staff and facilities, which are not available at all acute care facilities, or not available soon enough to preserve enough myocardial tissue in the wake of an MI. A significant effort has been undertaken in recent years to speed MI patients to the cath lab for PCI upon presenting, but these programs are not available everywhere, and even where available, do not often meet the 90 minute target of door to balloon time.
In the US, nearly 75,000 CAD patients annually present with atherosclerosis of the left main coronary artery (LMCA). The LMCA delivers oxygenated blood to 75% or more of the myocardium. An untreated, diseased LMCA results in 20% 1-year and 50% 7- to 10-year mortality rates. Historically, PCI of the LMCA (LMPCI) has been deemed too risky, however, recent advances in technique and tools have begun to allow an expanded LMCA patient population for PCI, especially in certain patient conditions where PCI is preferable to CABG (e.g., patients who are aging, delicate, and/or in critical condition).
The risks of LMPCI include prolonged myocardial ischemia from balloon inflations, “no-reflow phenomenon” (2-5% incidence rate), or coronary artery dissections (30% incidence rate). Existing circulatory support devices used to address these hemodynamic issues, such as the intra-aortic balloon pump (IABP) and left ventricle circulatory support devices (e.g., Impella 2.5), are unable to sufficiently meet the myocardium oxygen demands even though cardiac pumping mechanics are improved. The assistance from these devices is limited further during no-reflow and coronary artery dissection events. In addition, the clinically superior left ventricle circulatory support devices are complicated to use and require dedicated training and facilities, which has prevented wide-spread clinical adoption.
There are over 35,000 cardiogenic shock (CS) patients each year in the US. This condition severely complicates an MI event with in-hospital mortality rates exceeding 50 percent. PCI is the standard of care for these acute patients; however, the CS patient must be stabilized prior to intervention, according to ACC/AHA guidelines, using a short-term circulatory support device as a bridge. An IABP or left ventricle circulatory support device (e.g. Impella 2.5) can currently be utilized in these cases to stabilize the heart while awaiting revascularization.
The 200,000 S-T segment elevated MI (STEMI) patients per year in the US require immediate reperfusion of the myocardium. Thrombolytic medications are administered as the primary revascularization technique, however, 70 percent of those receiving thrombolysis fail to respond. Furthermore, 10 percent of those that initially respond to thrombolysis experience reocclusion while still an in-patient. These STEMI patients require clinically superior rescue PCI, as opposed to repeated thrombolysis.
Because only 1,200 out of 5,000 acute care hospitals are capable of performing PCI (and even fewer are capable of CABG), nearly 60 percent of STEMI patients do not achieve the required 90 minute time-frame for revascularization.
While awaiting revascularization, IAPB currently is the preferred circulatory assist device and is indicated for use by critical care unit (CCU), intensive care unit (ICU) and emergency medicine (ER) physicians in a variety of clinical settings. However, the IABP's use in MI events remains at less than 5 percent of cases due to complicated training and device-related malfunctions in 12-30% of all cases.
Circulatory support devices used in these cases have two major problems: inability to adequately augment blood flow in flow-limiting atherosclerotic coronary arteries to a damaged myocardium, and 12-30% device complication incidence rates, including peripheral ischemia, compartment syndrome, infection, hematological issues, and mechanical issues.